在后台执行查询时，如何显示加载图标？

<div id="loading-icon"></div>

#loading-icon {
  width: 40px;
  height: 40px;
  border: 4px solid #f3f3f3;
  border-top: 4px solid #3498db;
  border-radius: 50%;
  animation: spin 2s linear infinite;
}

@keyframes spin {
  0% { transform: rotate(0deg); }
  100% { transform: rotate(360deg); }
}

var loadingIcon = document.getElementById('loading-icon');
loadingIcon.style.display = 'block';

loadingIcon.style.display = 'none';